Solar tracker system

ABSTRACT

A photovoltaic system includes a collection of photovoltaic modules, a base supporting the collection of photovoltaic modules, and a damper coupled between the collection of photovoltaic modules and the base. The damper resists movement of the photovoltaic modules relative to the base. The damper has a first damping ratio when the collection of photovoltaic modules moves at a first rate relative to the base and a second damping ratio when the collection of photovoltaic modules moves at a second rate relative to the base, and the damper passively transitions from the first damping ratio to the second damping ratio.

CROSS-REFERENCE TO RELATED APPLICATION

This present application is a U.S. National Stage Entry of InternationalPCT Application No. PCT/US2019/017818, filed Feb. 13, 2019, which claimsthe benefit of U.S. Provisional Patent Application Ser. No. 62/629,931,filed Feb. 13, 2018. The aforementioned applications are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present application is related to solar tracker systems for solarpanels.

BACKGROUND

Photovoltaic (PV) power systems frequently track the sun to variousdegrees to increase an amount of energy produced by the system. Thesetrackers typically move photovoltaic modules to adjust an angle ofincidence of the sunlight on the surface of the PV modules. Inparticular, trackers typically rotate the PV modules around an axisprincipally oriented north to south, tilting the modules to as much as60 degrees towards the east and west and adjusting tilt within thisrange throughout the day. By tracking the position of the sun, PV powersystems often produce 20-30% more energy than fixed-tilt systems.

A common configuration of horizontal single-axis trackers (“SAT”) asdescribed above includes a single actuator near the center of a row ofPV modules, potentially with 80-120 modules tilted by a single actuator.The angle of tilt is defined by the position of the actuator, while atorque tube or other similar device transfers moments and positions therest of the row at this tilt. However, environmental loading (wind,snow, dead load, etc.) can twist portions of a row away from theintended tilt angle. This effect requires design considerations that addcost in order to decrease risk of failures.

To reduce row twist, some PV systems may have shorter row lengths ormore than one actuator per row. These approaches can reduce the risk ofsystem failure from excessive row twist, but may increase the PV systemcost as well as overhead and maintenance costs. Furthermore, whenmultiple actuators are used, the actuators within a row must communicatesuch that, for example, other actuators stop moving if one actuatorfails. This communication can be by electronic, mechanical, or othermeans. However, this active control brings additional failure modes thatmust be considered in the design of the PV system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a photovoltaic system, according to one embodiment.

FIGS. 2A-2C illustrate an example damper.

FIG. 3 illustrates an example Durst curve.

The figures depict various embodiments of this disclosure for purposesof illustration only. One skilled in the art can readily recognize fromthe following discussion that alternative embodiments of the structuresand methods illustrated herein can be employed without departing fromthe principles of the invention described herein.

DETAILED DESCRIPTION

FIG. 1 illustrates a photovoltaic (PV) system 100, according to oneembodiment. As shown in FIG. 1 , the PV system 100 may include acollection of PV modules 110, an actuator 120, a controller 130, and adamper 140. The PV system 100 is configured to generate electricity, andmay be used alone or with other similar photovoltaic systems in, forexample, a photovoltaic power station.

The collection of PV modules 110 includes an array of one or morephotovoltaic modules configured to convert solar energy into electricityby the photovoltaic effect. The collection of PV modules 110 isrotatably anchored to a base 115, and may be coupled to a power grid,battery, or other power transmission or storage system. The amount ofelectricity produced by each photovoltaic module can be a function of atleast the angle of incidence of light on the surface of the module,where more energy is captured when light is perpendicular to the surface(i.e., a zero-degree angle of incidence) than when light is incident athigher angles.

The actuator 120 is configured to rotate the collection of PV modules110 around one or more axes. The actuator 120 may be a linear actuatorcoupled to the PV module collection 110 and a fixed position, such asthe base 115. Increasing or decreasing the length of the linear actuatorchanges a tilt angle of the collection of PV modules 110 with respect tothe base 115. Other types of actuators may be used in other embodiments.For example, the PV module collection 110 may be mounted on an axle anda rotary actuator may drive the axle to rotate the collection of PVmodules 110 around an axis. In one embodiment, the actuator 120 rotatesthe collection of PV modules 110 around an axis centered at the base 115and geographically oriented substantially north to south, such that asurface of the PV module 110 can be tilted between east- and west-facingangles. The actuator 120 may also rotate the collection of PV modules110 around additional axes (e.g., an east-west axis), or thephotovoltaic system 100 may include one or more additional actuators tocause other movements of the collection of PV modules 110.

The controller 130 drives the actuator 120 to set a tilt angle of thecollection of PV modules 110. To increase the amount of energy capturedby the collection of PV modules 110, the controller 130 may set the tiltangle based on a position of the sun. In one embodiment, the controller130 is coupled to a light sensor (not shown in FIG. 1 ) to detect aposition of the sun during the day. As the day progresses, thecontroller 130 may drive the actuator 120 to move the PV modulecollection 110 to follow the detected movement of the sun. Thus, thecontroller 130 drives the actuator 120 to move the PV module collection110 from an orientation facing substantially east to an orientationfacing substantially west. Overnight, the controller 130 may drive theactuator 120 to return the collection of PV modules 110 to aneast-facing orientation in preparation for sunrise the next morning, orthe controller 130 may drive the actuator 120 to rotate the PV modulecollection 110 in response to detecting sunlight in the east. Thecontroller 130 may alternatively control the tilt angle of the PV modulecollection 110 without light feedback, for example based on time of day.

The damper 140 provides damping for the PV system 100, resistingmovement of the PV modules 110 relative to the base 115. Damping by thedamper 140 can mitigate dynamic wind loading or other vibrational loadsapplied to the PV system 100. Wind loading can induce motion in PVsystem 100, for example rotating the collection of PV modules 110 aroundthe base at a velocity multiple orders of magnitude higher than themotion induced by the actuator 120. Although the damper 140 is shown inFIG. 1 as a component separate from the actuator 120 for purposes ofillustration, the damper 140 may be incorporated into or positionedconcentric to the actuator 120.

The damper 140 has a variable damping ratio. The damper 140 can have atleast a first damping ratio under a first operating condition and asecond damping ratio under a second operating condition. Differentdamping ratios may be advantageous for different operating states. Forexample, a high damping ratio enables the damper 140 to dissipate moreenergy, and therefore better mitigates undesired oscillations of the PVsystem 100 under wind loading than a low damping ratio. A high dampingratio also potentially enables the damper 140 to bear a portion of thestatic load of the PV module collection 110 and dynamic loads caused byenvironmental conditions, reducing the load on the actuator 120.However, a high damping ratio may cause the damper 140 to provide enoughresistance to the movement of the actuator 120 cause the PV module 110to twist away from its intended orientation. As a result of the modifiedangle of incidence caused by this “propeller effect,” the collection ofPV modules 110 may generate less electricity. If twisted more than a fewdegrees, operation of the collection of PV modules 110 may fall outsideacceptable specifications. A low damping ratio, in contrast, reduces thetwist by providing lower resistance to movement of the actuator 120.

Accordingly, the damper 140 can have a first damping ratio while the PVmodules 110 move at a first rate. The damper 140 can have a seconddamping ratio, higher than the first damping ratio, during a secondmovement rate of the PV modules 110 that is higher than the first rate.For example, the damping ratio can be relatively low when the PV modules110 move at low speeds relative to the base 115 (e.g., while theactuator 120 is moving the collection of PV modules 110 without highenvironmental loading) and relatively high when the PV modules 110 moveat higher speeds relative to the base (e.g., under dynamic windloading). The higher damping ratio of the damper 140 may enable thedamper 140 to support a portion of the loading on the PV system 100,including the static load of the PV module collection 110 (e.g., theweight of the collection 110) and static or dynamic loading caused byenvironmental conditions such as wind, snow, or dust. The lower dampingratio reduces the damper's resistance to movement caused by the actuator120. The damping ratio of the damper 140 can change passively based onthe operating state of the actuator 120, such as the actuation rate. Thedamping ratio may therefore be adjusted without active control by, forexample, the controller 130.

The higher damping ratio can have a value greater than 1 (such that thePV system 100 is overdamped), while not fully locking up the PV system100 under loading by wind or other environmental conditions. That is,the damper 140 under the higher damping ratio allows some movement ofthe system 100 while providing resistance against that movement.However, in some embodiments, the damper 140 may fully lock up underhigh environmental loading.

FIGS. 2A-2C show one example damper 140. FIG. 2A is a bottom cutawayview of the damper 140, while FIGS. 2B-2C are a side cutaway view of thedamper. The damper 140 can include a damper piston 210 that can movethrough fluid contained in a damper chamber 205. Any fluid or mixture offluids can be contained within the damper chamber 205, such as air,water, or oil. The damper piston 210 includes at least two ports 215that, when open, allow fluid to flow between the damper piston anddamper chamber. The ports 215 are shown in FIG. 2A as being openings ina bottom end of the damper piston, but the ports can be located anywherein the damper piston.

The two ports 215 can include at least one smaller diameter port 215Aand at least one larger diameter port 215B. The larger diameter port215A can be controlled by a valve 220. When the damper piston 210 movesthrough the fluid at low speeds (e.g., while the PV modules 110 arerotated at a low speed by the actuator 120), the fluid can flow freelythrough the large diameter port 215B and provide little resistance tothe movement of the piston. FIG. 2B illustrates an example of the piston210 moving at a low speed through the fluid. As shown in FIG. 2B, thevalve 220 is open and fluid can pass through the larger diameter port215B to flow into or out of the damper piston 210. At higher speeds, thevalve 220 is pushed closed and the fluid is forced through the smallerdiameter port 215A. The resistance provided by the fluid flow throughthe small diameter port 215A increases the effective damping ratio ofthe damper 140. FIG. 2C illustrates an example of the piston 210 movingat a high speed through the fluid. As shown in FIG. 2C, the valve 220 isclosed and fluid is forced through the smaller diameter port 215A toflow into or out of the damper piston 210.

The damper 140 may have configurations other than that shown in FIGS.2A-2C and may passively regulate the damping ratio in other manners. Forexample, valves may regulate fluid flow through multiple equally ordifferently sized ports in the damper piston. At lower speeds, thevalves are open to allow the fluid to flow through several or all of theports. At higher speeds, the valves close the port and force the fluidto flow through a smaller number of ports. As another example, thedamper 140 may include a non-Newtonian fluid that has lower viscosity atlow piston speeds and higher viscosity at high piston speeds.

The PV system 100 may be designed based on wind speed in the area wherethe system will be installed. In particular, the PV system 100 may bedesigned to withstand expected peak loads from the area's windconditions following a protocol such as ASCE 7. FIG. 3 illustrates anexample Durst curve, which relates average wind speed to gust duration,that may be used in such protocols. As shown in FIG. 3 , average windspeeds are higher for shorter measurements of gust duration than forlonger measurements. Because the damper 140 has a higher damping ratiounder wind loading and bears a portion of the load on the collection ofPV modules 110, the PV system 100 may be designed based on longer gustdurations—and therefore lower wind speeds—than photovoltaic systemslacking the damper 140. Furthermore, while the Durst curve shown in FIG.3 assumes free, unobstructed wind speed, the PV system 100 will likelyexperience turbulent air flow as dynamic winds move around thestructure. The average moments on the PV system 100 under turbulent flowmay be even lower across longer gust durations than predicted by theDurst curve. Accordingly, at least one of the base 115, the actuator120, and the PV modules 110 can be designed to withstand an averagevalue of moments applied to the PV system 100 across a specifiedduration of time. This duration of time can be calculated based on windtunnel testing, and can be, for example, approximately equivalent to aresponse time of the PV system 100 under target environmental loads. Thedesign for lower wind speeds may reduce the amount of material used toconstruct the base 115, the actuator 120, and the collection of PVmodules 110, and may reduce overhead and maintenance costs for the PVsystem 100.

In some embodiments, the higher damping ratio of the damper 140 isdesigned under wind tunnel testing to achieve a specified response timeof the PV system 100 under high environmental loads. Because the higherdamping ratio resists movement of the actuator 120, it may take longerfor the actuator 120 to move the PV modules 110 to a specified angleunder the higher damping ratio than under the lower damping ratio. Thehigher damping ratio can be selected such that the movement of the PVmodules 110 through a designated angular distance (relative to the base115) will take a specified amount of time if the PV system 100 issubjected to a specified amount of wind loading that is enoughenvironmental loading to cause the damper 140 to transition to thehigher damping ratio. For example, the higher damping ratio can beselected under wind tunnel testing such that the actuator moves the PVmodules 110 thirty degrees relative to the base in 60 seconds while thePV system 100 is subjected to a specified amount of wind loading above athreshold wind speed. The higher damping ratio can be selected to allowfaster or slower movements of the PV modules 110, such as 10 seconds, 30seconds, or 120 seconds.

Other Considerations

The foregoing description of various embodiments of the claimed subjectmatter has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit the claimedsubject matter to the precise forms disclosed. Many modifications andvariations can be apparent to one skilled in the art. Embodiments werechosen and described in order to best describe the principles of theinvention and its practical applications, thereby enabling othersskilled in the relevant art to understand the claimed subject matter,the various embodiments, and the various modifications that are suitedto the particular uses contemplated.

While embodiments have been described in the context of fullyfunctioning computers and computer systems, those skilled in the art canappreciate that the various embodiments are capable of being distributedas a program product in a variety of forms, and that the disclosureapplies equally regardless of the particular type of machine orcomputer-readable media used to actually effect the distribution.

Although the above Detailed Description describes certain embodimentsand the best mode contemplated, no matter how detailed the above appearsin text, the embodiments can be practiced in many ways. Details of thesystems and methods can vary considerably in their implementationdetails, while still being encompassed by the specification. As notedabove, particular terminology used when describing certain features oraspects of various embodiments should not be taken to imply that theterminology is being redefined herein to be restricted to any specificcharacteristics, features, or aspects of the invention with which thatterminology is associated. In general, the terms used in the followingclaims should not be construed to limit the invention to the specificembodiments disclosed in the specification, unless those terms areexplicitly defined herein. Accordingly, the actual scope of theinvention encompasses not only the disclosed embodiments, but also allequivalent ways of practicing or implementing the embodiments under theclaims.

The language used in the specification has been principally selected forreadability and instructional purposes, and it cannot have been selectedto delineate or circumscribe the inventive subject matter. It istherefore intended that the scope of the invention be limited not bythis Detailed Description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of variousembodiments is intended to be illustrative, but not limiting, of thescope of the embodiments, which is set forth in the following claims.

What is claimed is:
 1. A photovoltaic system, comprising: a collectionof photovoltaic modules; a base supporting the collection ofphotovoltaic modules; and a damper coupled between the collection ofphotovoltaic modules and the base and resisting movement of thecollection of photovoltaic modules relative to the base, the damperhaving a first damping ratio when the collection of photovoltaic modulesmoves at a first rate relative to the base and a second damping ratiowhen the collection of photovoltaic modules moves at a second raterelative to the base, wherein the damper passively transitions from thefirst damping ratio to the second damping ratio.
 2. The photovoltaicsystem of claim 1, further comprising an actuator coupled to thecollection of photovoltaic modules and configured to move the collectionof photovoltaic modules to change an angle of the collection ofphotovoltaic modules relative to the base.
 3. The photovoltaic system ofclaim 2, wherein the actuator moves the collection of photovoltaicmodules at the first rate.
 4. The photovoltaic system of claim 3,wherein environmental loading moves the collection of photovoltaicmodules at the second rate, and wherein the second damping ratio ishigher than the first damping ratio.
 5. The photovoltaic system of claim2, further comprising a controller in electronic communication with theactuator and configured to drive the actuator to move the collection ofphotovoltaic modules relative to the base, wherein the dampertransitions from the first damping ratio to the second damping ratioindependently of the controller.
 6. The photovoltaic system of claim 1,wherein the damper supports at least a portion of a load placed on thephotovoltaic system by an environmental condition.
 7. The photovoltaicsystem of claim 1, wherein the second damping ratio is greater thancritical damping of the photovoltaic system.
 8. The photovoltaic systemof claim 7, wherein the second damping ratio causes the damper to befully locked against the movement of the photovoltaic modules relativeto the base.
 9. The photovoltaic system of claim 7, wherein the seconddamping ratio causes the damper to permit movement of the photovoltaicmodules relative to the base while resisting the movement.
 10. Thephotovoltaic system of claim 1, wherein the damper comprises: a damperchamber containing a fluid; a damper piston configured to move throughthe fluid relative to the damper chamber; a first port in the damperpiston, the first port having a first diameter; a second port in thedamper piston, the second port having a second diameter larger than thefirst diameter; and a valve configured to open or close the second portsuch that the second port is open when the collection of photovoltaicmodules moves at the first rate relative to the base and the second portis closed when the collection of photovoltaic modules moves at thesecond rate relative to the base, wherein the fluid contained in thedamper chamber flows between the damper chamber and damper pistonthrough both the first and second ports when the second port is open andonly through the first port when the second port is closed.
 11. Thephotovoltaic system of claim 1, wherein the second damping ratio allowsthe collection of photovoltaic modules to move a designated angulardistance relative to the base in a specified amount of time underspecified wind loading.
 12. A photovoltaic system, comprising: one ormore photovoltaic modules; a base coupled to the one or morephotovoltaic modules and supporting the one or more photovoltaicmodules; an actuator coupled to the one or more photovoltaic modules andconfigured to move the one or more photovoltaic modules to dynamicallychange an angle of the one or more photovoltaic modules with respect tothe base; and a damper coupled between the one or more photovoltaicmodules and the base and resisting movement of the one or morephotovoltaic modules relative to the base, the damper having a firstdamping ratio when the actuator moves the one or more photovoltaicmodules and passively transitioning to a second damping ratio that isgreater than the first damping ratio when environmental loads areapplied to the one or more photovoltaic modules.
 13. The photovoltaicsystem of claim 12, further comprising a controller in electroniccommunication with the actuator and configured to drive the actuator tomove the one or more photovoltaic modules relative to the base, whereinthe damper transitions from the first damping ratio to the seconddamping ratio independently of the controller.
 14. The photovoltaicsystem of claim 12, wherein the damper supports at least a portion of aload placed on the photovoltaic system by an environmental condition.15. The photovoltaic system of claim 12, wherein the second dampingratio is greater than critical damping of the photovoltaic system. 16.The photovoltaic system of claim 15, wherein the second damping ratiocauses the damper to be fully locked against the movement of thephotovoltaic modules relative to the base.
 17. The photovoltaic systemof claim 15, wherein the second damping ratio causes the damper topermit movement of the photovoltaic modules relative to the base whileresisting the movement.
 18. The photovoltaic system of claim 12, whereinthe damper comprises: a damper chamber containing a fluid; a damperpiston configured to move through the fluid relative to the damperchamber; a first port in the damper piston, the first port having afirst diameter; a second port in the damper piston, the second porthaving a second diameter larger than the first diameter; and a valveconfigured to open or close the second port such that the second port isopen when the one or more photovoltaic modules moves at a first raterelative to the base and the second port is closed when the one or morephotovoltaic modules moves at a second rate relative to the base,wherein the fluid contained in the damper chamber flows between thedamper chamber and damper piston through the second port when the secondport is open and through the first port when the second port is closed.19. The photovoltaic system of claim 12, wherein the second dampingratio allows the one or more photovoltaic modules to move a designatedangular distance relative to the base in a specified amount of timeunder specified wind loading.
 20. The photovoltaic system of claim 12,wherein at least one of the photovoltaic modules, the base, or theactuator is designed to withstand an average value of moments applied tothe photovoltaic system across a specified period of time.